A magnetic polymer is a composite material composed of polymer and magnetic inorganic compound. Currently, most magnetic polymers in fastest development are required in a particle form and sized between nanometers and millimeters. Since magnetic polymers are capable of rapidly moving in a certain direction in an external magnetic field, they are widely applied in fields such as biochemistry, molecular biology, medical science, pharmaceutical science and chemical catalysis, etc, for example, they may act as powerful isolation and purification tools in studies on purification and isolation of nucleic acids and proteins, cell screening, immune analysis and clinical diagnosis, and may also used in targeting drugs. The magnetic polymer is not limited to spherical shape, which can be any geometric shape, and it may assume various kinds, including solid, hollow, porous, dumb bell-shaped, onion-shaped, micro capsular, flaky or other irregular shapes, etc.
A magnetic polymer mainly comprises two parts: one is the magnetic part, mainly a kind of inorganic particles, for example metal particles such as iron, cobalt and nickel, etc, or magnetic ferrite particles, for example γ-Fe2O3 and MFe2O3, where M may be Fe, Zn, Mg, Cu, Ca, Ba, Sr, Ni, Co, Mn, etc. Another part of the magnetic polymer is the polymer, and typically the magnetic particles are encapsulated inside the polymer.
Currently, the known methods for preparing a magnetic polymer are to assemble the inorganic particle part and the polymer part sequentially, which can be summarized in the following kinds.
{circle around (1)} preparing in advance the magnetic particles and polymers, physically mixing the polymers and magnetic particles. This method is simple and less demanding, but the product is poor in shape, with wide distributions of particle diameters.
{circle around (2)} preparing in advance the magnetic particles, and polymerizing organic monomers at the periphery of the magnetic particles. Since the inorganic particles and the organic monomers have a poor affinity, the greatest difficulty for preparing composite polymers using the organic monomer polymerization method on magnetic particles is that the monomers are hard to be polymerized at the surface of inorganic particles, but form spheres separately, which may result in vacant spheres, and the magnetic particles are unevenly distributed between spheres either. To overcome this drawback, it is necessary to process the surface of inorganic particles, but the product still can not meet the requirement.
{circle around (3)} preparing in advance the polymer firstly, introducing magnetic particles into the polymer. For example, U.S. Pat. No. 4,774,265 discloses a method of preparing the polymer parent substance with very even particle diameters first, and then introducing the magnetic substances into the inside of the polymer. The method requires the polymer to have functional groups capable of binding metal ions such as Fe, Co, and Ni, and only in the case where the unabsorbed ions in the solution are eliminated after absorbing sufficient divalent metal ions and Fe3+ ions with suitable proportions, and alkaline reagents are added finally, the magnetic particles can be generated inside the polymer in situ. If a polymer has no absorption capability to the above metal ions, such polymer can not be used to prepare magnetic polymer.
The method disclosed by the U.S. Pat. No. 4,774,265 is to add a solution of a mixture of two metal ions into the polymer microsphere. This method requires the polymer microsphere to absorb divalent metal ions and Fe3+ ions with a suitable proportion at the same time, and for oxidation-reduction reaction, the amount of the oxidization agent or reducing agent may be controlled such that the final proportion between the divalent metal ions and Fe3+ ions is 1:2, and thereby generating magnetic Fe3O4.
However, to the polymer which has no oxidable or reducible group, use of such mixed iron salt does not have a good effect in the following aspects: firstly, it is not easy to control the absorption proportion of the divalent metal ions and Fe3+ ions inside the polymer to be exactly 1:2; secondly, a proportion of metal irons in mixed iron salt, which is suitable for one polymer, may not be suitable for another polymer B; thirdly, it may require times of repetitive operations to obtain the magnetic transfer effect, and moreover, magnetic polymer can often not be obtained for micron or smaller polymers.
Besides, introduction of magnetic particles to carboxylic resin is disclosed in the literature “Study on Preparing Magnetic Cation Exchange Resin by Chemical Transformation Method”, by Zhang Mei, Wang Busen, Zhang Yuge, He Binglin, etc, Ion Exchange and Absorption, 1995, 11 (4), 302-308, wherein in case the mol ratio between two iron salts being 2:1, or even 1:1, it is unable to introduce magnetic particles into the polymer, which can only be successful under the mol ratio being 1:5-1:50, and the polymer can only exhibit a strong magnetism after repeating the introduction three times or more. It is speculated that weak acid type ion exchange resin has a clear selectivity, which has a strong absorption capability to Fe3+, but weak to absorb Fe2+, thus it needs a greatly excessive amount of Fe2+ salt in the mixed iron salt. Besides, when magnetic transferring, the increase of magnetism is not proportional, and there may have more complex affecting factors besides the selectivity.
Besides, the information as disclosed in Example 2 of the U.S. Pat. No. 4,783,102 also shows a similar situation, wherein when using a 1:1 iron salt mixture solution, a sulfonated cross-linked polystyrene ion-exchange resin having a strongly acidity only has a slight magnetism after the first magnetism transformation, and only exhibits an apparent magnetism after times of magnetism transformation.
Thus, a method which is simpler, wider in application and more operable is needed.